Posted
by
Zonk
on Sunday March 04, 2007 @03:40PM
from the journey-to-the-top-of-the-earth dept.

eldavojohn writes "A group of scientists are disembarking right now to study an open gash in the ocean floor where earth's mantle lays exposed without any crust covering it. The scientists describe this as the result of the mantle moving too quickly for the crust to keep up. Either that, or the mantle was never covered by the crust and just has always been like this. From the article, 'Regardless of how they formed, the exposed mantle provides scientists with a rare opportunity to study the Earth's rocky innards. Many attempts to drill deep into the planet barely get past the crust.'"

If i recall my school years correctly, the mantel is made of rock, not magma. In between the crust and mantle is the lithosphere (or whatever its called) that contains all the magma. I would assume that since crust hasent formed, there is no magma around there, which i would ask, why is that?

You're right magma + coolant (water) = rock. The mantle is a section of the planet, comprised of different materials than the crust. This an opportunity to look at those materials without having to drill do far. Trust me, not many scientists was to be looking at 2000 degree molten rock up close.

There's a lot of other cool things we can see while we're down there, like how the rock crystals formed under that kind of pressure and how fast they cooled. All kinds of cool things can be interpreted by the rocks crystalline structure.

Mantle rock is not magma. Mantle material is usually very hot because it is (A) very heavy, and (B) usually covered by a layer of insulating lighter crust material. The crust is 3-18 miles thick. Magma is usually crust material that got pushed down into hot mantle material and melted. The crustal material magma being lighter than mantle wants to rise above the mantle magma. So usually we have an intrusion of lighter crustal magma being forced through the mantle. So we've never seen mantle material exposed before. Some small samples of solid mantle material have been carried up by some of the cooler type volcanoes. This is how we get diamonds and peridots. Read about Kimberlite pipes.

Thanks for the pointer, ElectricRook. I read all about Kimberlite Pipes [amnh.org] and now I'm excited by the prospect of "unearthing" a motherlode of diamonds on the sea floor! Perhaps these scientists have embarked, or disembarked, on that rare beast -- science with an immenent financial payoff.

There are apparently diamonds almost everywhere, or some people think. Here in Northern California, they are reported to be found near where gold was discovered in Placerville California (Actually Smith Flat). I found what appears to be a kimberlite pipe in Northern Oregon. This is kind of a unique area, where volcanic islands were partially subducted and merged with the Coast. I don't know if diamonds will be found there, I've read they only appear in any meaningful quantities in about 2% of Kimberlite

You can get UV LEDs these days. Just swap the white LEDs in a flashlight with a bunch of UV ones. I'd also put a violet LED in there just as a reminder (I think they're white ones with filters, but anyway.)

I recall that small black diamonds were found in placer deposits in North Carolina. IIRC, supposedly the state of affairs then was that they didnt' even know if the diamonds were directly eroded from a kimberlite deposit or if they had subsequently been embeded in sedimentary rock and reeroded.

Good luck with that kimberlite pipe (and perhaps others like it). I figure any serious diamond deposits would have been discovered by now due to the extreme amount of gold panning that has gone on. However, as I rec

All the gold in California lies in "A bank in middle of Beverly Hills in somebody else's name".

Oh wait back to the topic...

Most of the gold in California lies in "The Motherlode" mining district below 5,000' elevation between Downeyville, and Yosemite. It occupies just about all the streams in that region. Plus there is a north-south seam between Auburn and Jackson where we find the really deep hard rock mines (several thousand feet deep) There they mine gold bearing milky quartz in granite (only one min

I have heard a theory that the gold was emitted by the mid oceanic ridge, and deposited on the sea floor. That sea floor was smashed onto the edge of California by accretion something like 250MYA (Million Years Ago). A lot if it was mixed into magma which intruded into the accreted crust as granite plumes, the gold being concentrated in quartz veins. The band being a portion of the sea floor that was not sub ducted, but instead acreted into the crust.

It's apparently not a constant thing, but highly fluxuating, at one time 250MYA, it was a large quantity of gold, ocean floor measurements will tell what it is today. There is apparently a lot of mineral nodules on the abyssal planes.

Maybe it's nothing but 250 million years ago was the end of the Permian Era and the time of the Great Dying. Might have been some weird ocean floor chemistry from that time. But gold isn't very soluable in water until the temperature gets to around 300 degrees celsius (IIRC). Minute amounts of gold in the bedrock dissolve and deposit where the temperature drops to below the soluable temperature. So it's a matter of local conditions (ie, there has to be some gold in the bedrock before it can dissolve and red

I've yet to RTFA yet but, I've one or too points to make...You're statment "Magma is usually crust material that got pushed down into hot mantle material and melted." is not entirely accurate.In subduction zones where crustal material gets pulled down in to the mantle the melting is very often that of the mantle between the subducted and the subducting crustal slabs. The subducted slab carries a lot of water and as it heats the water is released in to the mantle, this changes the melting temperature of th

I hate all this 0==false/otherwise==true crap. It makes for some really unreadable code. Is it really that much more effort to make a boolean var with a meaningful name? I expect a compiler would optimise it out easily...

The mantle is a solid, albeit warm and plastic, material. It's solid because of the immense pressure the material is under. Brought up via plate tectonics, the material can melt as the pressure is released.

They are disembarking from their port of origin, and embarking on a mission to study the ocean floor gash. The summary used the word correctly. s/disembarking/embarking/ without changing anything else in the summary would result in something that didn't make sense.

>They are disembarking from their port of origin, and embarking on a mission to study the ocean floor gash.

The first part of this sentence would make sense only if disembark meant to set out on a journey. It actually means to get off a barque which is a type of ship. It is frequently used loosely to mean to get off any ship or even any large conveyance. But it never means to set out on a journey.

The second part of the sentence is probably correct since they will most certainly have to get on a ship in

The first part of this sentence would make sense only if disembark meant to set out on a journey.

"They are disembarking from their port of origin." -> "They are setting out on a journey from their port of origin." Ok, that would work. But that isn't the false meaning of disembark I really had in mind. I was thinking more like (first sentence) -> "They are leaving their port of origin." This also works.

Cuz I'm praying for rain
And I'm praying for tidal waves
I wanna see the ground give way.
I wanna watch it all go down.
Mom please flush it all away.
I wanna see it go right in and down.
I wanna watch it go right in.
Watch you flush it all away.

'Regardless of how they formed, the exposed mantle provides scientists with a rare opportunity to study the Earth's rocky innards. Many attempts to drill deep into the planet barely get past the crust.'

Barely get past the crust? So they do get past the crust? Then how is exploring this bit of mantle different from exploring the parts we've drilled to?

A few months ago I was wondering how deep mankind has drilled, and found some interesting [damninteresting.com] stuff [wikipedia.org]. Basically, you should read "barely" as "didn't".

As always, when you think something's easy (make_small_hole(); while(1) { make_hole_deeper(); } ), it's just because your ignorance doesn't let you appreciate the problems, like the extreme temperature and pressure. For example, I didn't realize that the pressure compresses the rocks and when you drill a hole that deep, the rocks around it want to expand, causing engineering nightmares.

And while measuring the straightness of a hole seems quite doable (or put otherwise, I accept the assumption that there exists technology to do that), I still wonder how they can adjust the drilling direction.

If you read Robert Ballard's autobiography, or one of many other books on oceanography, you'll find that plate tectonics only started to become accepted as a credible theory in the 1960s, with many significant researchers still dismissing the theory in the early 1970s.

To put that in context: people had visited the moon before plate tectonics was widely accepted.

Since then there has been research, including drilling, but it is probably fair to say they mankind still only has a pretty fuzzy picture of what is

The shrinkage of the hole isn't the only problem and could partly be overcome by taking a larger drillhead than the drillshaft (or tube or whatever connection between the higher part and the drillhead).
If you take a really long straw and place it vertically in your beverage, you can only lift the water so much before the weight of the water becomes higher than you could lift by sucking your mouth vacuum.
This same effect happens with the rock deposit you drill up. You need to remove it to somewhere, and th

or the time cube
http://www.timecube.com/ [timecube.com]
Is this the genetic religosity thread, i'm lost in tequila and beer?
Cop scanner:
Thir'is is a large goat in the road. Cops removing equestrians from the roadway.
Is a goat a equestrian?

"Many attempts to drill deep into the planet barely get past the crust."
I wasn't aware of any drilling that has past the crust. The deepest I knew about was the Kola Borehole [wikipedia.org] which only reached 12,262 meters. I understand drilling the seafloor saves us time and depth but I wasn't away of anyone getting through the crust yet.

...and the beginning of the Space Age. There was an attempt to drill past the crust to the mantle in a spot where the transition came up fairly close to the Earth's surface, called Project Mohole http://www.nas.edu/history/mohole/ [nas.edu]. This referred to the Mohorovicic Discontinuity, or "Mohole". The IGY was an early attempt at an international cooperative effort in Earth studies.

The importance of this effort was underlined by the fact that Walt Kelly's "Pogo" sent it up. Since the event was a "year" of 18 months, Pogo suggested naming the extra months after foods -- Octoberry, Novemberry etc.

In a side note, the US response to Sputnik included a science payload named Nora-Alice 1, beacon transmitter for Discoverer satellite, which took it's name from a poem Pogo wrote in honour of the IGY. http://www.ece.uiuc.edu/about/history/reminiscence /space.html/ [uiuc.edu] has a picture and a small quote down the column a bit.

So as you can see, drilling a hole in the Earth past the crust to the mantle inspired some of the first orbital satellites. Remarkable! Oh, and then there was LAGEOS, of course, but I'll let you look that one up.

While my brother was in high school one of his classmates winged it during a class where they had to read their book reports. This guy made up a book called "The Moho Menace" where hostile creatures attack the surface after being released by drilling to the moho discontinuity.

Col. Robert Iverson: People. Doctors Zimsky and Keyes? You guys are our resident geophysicists, so what do you make of this?Dr. Conrad Zimsky: The mantle is a chemical hodgepodge of, a, variety of elements...Dr. Ed 'Braz' Brazzelton: Say it with me: "I don't know."

Yuck. That's even worse. And it's also ironic that you feel the need to refer to people with an understanding of current environmental issues as 'tree-huggers' when trees are pretty much the only thing you and your users could hug without getting slapped.